共查询到20条相似文献,搜索用时 31 毫秒
1.
M. L. Shah R. C. Das P. K. Mandal D. R. Rathod Vas Dev K. G. Manohar B. M. Suri 《Pramana》2010,75(6):1141-1144
We report the measurement of photoexcitation cross-sections of three first-step uranium transitions (0 → 16900.38 cm −1, 0 → 17361.89 cm −1 and 620 → 17361.89 cm −1) using saturation method. These measurements were performed on a resonance ionization mass spectrometry (RIMS) set-up consisting
of Nd:YAG-pumped dye lasers, a reflectron time-of-flight mass spectrometer and high-temperature atomic vapour source. The
uranium vapours were excited and photoionized by two-colour, three-photon photoionization scheme using Nd:YAG-pumped dye laser
system. The resultant photoion signal was monitored as a function of dye laser fluence used for first step excitation to measure
the excitation cross-section values. A new approach was adopted to overcome the large uncertainties associated with such measurements.
With this approach the cross-section of transitions whose value is already reported in the literature was measured as a bench
mark. By normalizing the measured value to the reported value, a scaling factor was derived. This scaling factor was used
to scale up the cross-section values of other transitions measured by this method. 相似文献
2.
Expressions for the screening length and the ambipolar diffusion length are derived, for the first time, for the case where hopping conduction and band conduction coexist in semiconductors with hydrogen-like impurities. A method is proposed for calculating the diffusion coefficient of electrons (holes) hopping between impurity atoms from data on the Hall effect, in the case where the hopping and band conductivities are equal. An interpretation is given of available experimental data on hopping photoconduction between acceptors (Ga) and donors (As) in p-Ge at T=4.2 K doped by a transmutation method. It is shown that the relative magnitude of the mobilities of electrons hopping between donors and holes hopping between acceptors can be found from the hopping photoconductivity measured as a function of the intensity of band-to-band optical carrier excitation. 相似文献
3.
The kinetics of recombination of electrons and acceptor-bound holes in AlGaAs-GaAs heterostructure obey a single-exponential
decay in the liquid phase of 2D electrons, whereas localization gives rise to a broad spectrum of recombination rates, especially
in the magnetic freeze-out regime. This results in a power-law dependence I(t)∝(τ/t)α in the tail of the recombination kinetics, with the universal exponent α=(1−ν)−1 at ν<1 for all the samples examined experimentally in this work.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 118–122 (25 January 1996)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
4.
Summary Elastic and inelastic collisions of fast non-relativistic electrons with positronium atoms have been studies in the Born-Ochkur
approximation. It has been shown that exchange plays an important role for transitions between states with the same parity
as in this case the direct scattering amplitude vanishes. Numerical results for the total and ortho-para conversion cross-sections
for the 1s→1s, 1s→2s and 1s→2p transitions have been presented for projectile energies varying from 0.1 to 10 keV. According to charge symmetry, presented
results apply also to positron projectiles. 相似文献
5.
Yu. P. Sukhorukov N. N. Loshkareva A. S. Moskvin V. L. Arbuzov A. S. Ovchinnikov N. M. Chebotaev A. A. Samokhvalov 《Physics of the Solid State》1997,39(12):1916-1920
The optical absorption spectra of single-crystal CuO bombarded with 5-MeV electrons exhibit reduced absorption in the region
of the fundamental absorption edge at 17 eV, which corresponds to the b
1g
→e
u transition with charge transfer in CuO
4
6−
. A simultaneous increase in absorption is observed in the middle infrared and in the region of high energies centered on
2.9 eV. The experimental results obtained are interpreted in terms of ideas on the phase-inhomogeneous nano-agglomorated structure
in copper oxides that occurs as a result of the nucleation of polar centers (CuO
4
5−
, CuO
4
7−
) under electron bombardment.
Fiz. Tverd. Tela (St. Petersburg) 39, 2141–2146 (December 1997) 相似文献
6.
Yu. I. Man’kov 《Physics of the Solid State》1999,41(4):582-588
The effect of conduction electrons on the magnetization curve of a metallic ferromagnet with surface pinning of the magnetic
moment is investigated theoretically. The electronic contribution is due to the rearrangement of the discrete spectrum of
charge carriers trapped by the nonuniform magnetic induction of such a ferromagnet, and it is a kind of diamagnetic effect
that appreciably decreases the volume-averaged magnetization of the ferromagnet. A powerlaw dependence H
−3/4 on the external magnetic field H is obtained according to the law of magnetization approach to saturation. This dependence is due to the contribution of the
conduction electrons.
Fiz. Tverd. Tela (St. Petersburg) 41, 647–653 (April 1999) 相似文献
7.
R. Ebert H. Pascher G. Appold H. G. Häfele 《Applied Physics A: Materials Science & Processing》1977,14(2):155-159
We report for the first time stimulated magneto-Raman scattering inp-type InSb. Two different Raman scattering processes were observed. The first one has a Raman shift of about 2cm−1/kG and is observed at magnetic fields up to 30kG. The other one is observable only at high magnetic fields above 30kG and
shows Raman shifts between 1.2cm−1 and 3.0cm−1 with a tuning rate of about 0.2cm−1/kG. The first process can be interpreted either as spin-flip Raman scattering by photo-excited electrons in the conduction
band or as Raman scattering by holes in the valence band involving transitions from heavy to light hole states. The other
Raman shift observed seems to occur on account of transitions between the heavy hole ladders. 相似文献
8.
K. B. Korotchenko Yu. L. Pivovarov T. A. Tukhfatullin E. I. Fiks 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2010,4(5):823-830
It is shown that, in contrast to diffracted channeling radiation (DCR) in the case of planar channeling, transitions of type
2 → 1, 3 → 2, 4 → 3, and so on make the main contribution to DCR in the case of axial channeling along an isolated axis. The
angular DCR distributions for channeling of electrons with the energy corresponding to the Lorentz factor γ = 100 are calculated
for an isolated axis using the Coulomb-type potential. 相似文献
9.
Two well-known models for calculating the critical density N
C of a metal-insulator transition, as a function of the Bohr radius a
H of an isolated impurity as temperature T→0 K, are refined by making allowance for the screening of ions by electrons hopping along impurities. In one model, the transition
at N
C1 is explained by the appearance of delocalized electrons as the impurity band is displaced into the allowed-energy band as
a result of a decrease in the electron (hole) affinity of ionized impurities. In the other model the transition is explained
by an unbounded increase in the static permittivity of the crystal as the density of impurity atoms increases to N
C2. The obtained approximations N
C1
1/3
a
H≈0.24 and N
C2
1/3
a
H≈0.20 for the degree of compensation K=0.01 describe existing experimental data for 1<a
H<10 nm.
Fiz. Tverd. Tela (St. Petersburg) 40, 147–151 (January 1998) 相似文献
10.
Polishchuk AV Karaseva ET Emelina TB Cramariuc O Karasev VE 《Journal of fluorescence》2011,21(6):2117-2122
Electronic absorption, luminescence, IR and Raman spectra of polymorphous forms of fluoroquinolones were investigated. Assignment
of the band maxima due to π→π* and n→π* electronic transitions were done. The structural changes are responsible for the absorption
band modifications. One-electron transitions in the long wavelength region, excitation wavelengths, oscillator strengths and
involved molecular orbitals for the zwitter-ionic and cationic protonated forms for different fluoroquinolones were calculated
with quantum-chemical and molecular dynamic methods. The electron density redistributions on the FQs separate fragments during
the photoexcitation to the S1*-state were carry out by Mulliken calculations. It was shown that the degree of neutral and zwitter-ion FQs penetration through
the bacterium membrane is different. 相似文献
11.
12.
L. E. Vorob’ev D. V. Donetskii D. A. Firsov E. B. Bondarenko G. G. Zegrya E. Towe 《JETP Letters》1998,67(7):533-538
Terahertz emission accompanying heating of two-dimensional electrons by a strong electric field applied along size-quantized
GaAs/AlGaAs layers is observed and investigated. The emission is due to indirect optical transitions of hot electrons in the
bottom size-quantization band. The experimentally obtained emission spectra are compared with the spectra calculated taking
into account scattering of electrons by optical phonons, impurities, and interfacial roughness and electron-electron scattering.
Satisfactory agreement is obtained. The temperature of the hot electrons is determined from a comparison of the spectra.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 7, 507–511 (10 April 1998) 相似文献
13.
The motion of a particle in a metallic crystal is studied for low temperatures where transitions between adjacent interstitial
sites are caused by quantum tunneling. The influence of electrons and phonons on the hopping rate is taken into account by
means of a functional integral method. The electronic influence may effectively be described by Ohmic damping which dominates
the low temperature behavior of the defect motion. When subsequent tunneling transitions are statistically independent, the
diffusion constant is found to obey a power law, D∼T2K−1, where K depends on the defect-electron interaction. This power law is limited at low temperatures by the effects of phonon
excitations. Near the transition between electron and phonon dominated behavior the diffusion constant has a minimum where
the precise temperature dependence of the rate depends not only on phonon spectra but also on the processes limiting phonon
lifetimes. 相似文献
14.
Ya. E. Pokrovskii O. I. Smirnova A. Khvalkovskii 《Journal of Experimental and Theoretical Physics》1997,85(1):121-129
The lifetime of charge carriers in the lowest excited states of some impurities of groups III and V in diamond, silicon, and
germanium can be several (four to six) orders of magnitude longer that the lifetime of free carriers. Accumulation of carriers
in these long-lived states may give rise to several new effects, such as hopping photoconductivity via long-lived excited
states of impurities in dc and microwave electric fields, slow relaxation of induced absorption, and infrared absorption at
energies lower than the impurity ionization energy.
Zh. éksp. Teor. Fiz. 112, 221–236 (July 1997) 相似文献
15.
A. Lushchik Ch. Lushchik I. Kudryavtseva A. Maaroos F. Savikhin E. Shablonin E. Vasil’chenko 《Optics and Spectroscopy》2011,111(3):434-440
The processes of photon multiplication in insulators have been considered. The luminescence of Tb3+ ions (5
D
3 → 7
F
J
, 5
D
4 → 7
F
J
transitions) upon intracenter excitation, the optical excitation of oxyanions, or the formation of separated electrons and
holes has been studied for CaSO4 doped with Tb3+ and Na+ ions at 6–9 K. An increase in Tb3+ concentration from 0.2 to 4 at % and transition from single Tb3+-Na+ states to centers that contain two or three terbium ions leads to the redistribution of the luminescence intensities in favor
of the 5
D
4 → 7
F
J
transitions and increase in their efficiency due to the possibility of the cooperative 5
D
3 → 5
D
4 and 7
F
6 → 7
F
J
transitions and the 4f
75d
1 → 5
D
3 and 7
F
6 → 5
D
4 transitions in the two- and three-terbium centers. Based on the example of MgO single crystals with highly mobile excitons,
holes, and electrons, the migration of free excitons and holes toward Cr3+ ions in the crystal bulk and their exit from the bulk to the surface have been revealed at 9 K. Surface losses limit the
luminescence quantum yield of MgO:Cr3+, CaSO4:Tb3+, and many other materials. 相似文献
16.
The quantum-well D(−)-states in the presence of magnetic field longitudinal with respect to the growth axis are considered.
Within a model of zero-radius potential, an equation is derived that determines the dependence of the D(−)-state binding energy on the parameters of the potential of the structure, coordinates of the D(−) center, and the magnetic field. The results are compared with the experimental dependence of the D(−)-state binding energy on the magnetic field and the data are shown to be in good agreement with calculations for magnetic
fields B < 10 T. A dimension factor is defined in the dependence of the binding energy on coordinates for the 2D → 1D → 0D transition.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 25–29. 相似文献
17.
A. P. Serebrov 《JETP Letters》1996,63(1):1-6
It is shown that a two-step model of the reaction pd→3HeX (X=η, η′ eω, φ), involving the subprocesses pp) →dπ+ and π+
n→Xp, can account for the form of the energy dependence of experimental cross sections above the thresholds under the assumption
that the singlet part of the pp→dπ+ amplitude dominates. The spin-spin asymmetry for the reaction dp→3HeX has been found to be ∼;−1 in the forward-backward approximation.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 1, 3–7 (10 January 1996)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
18.
V. A. Kul’bachinskii I. A. Churilov P. D. Mar’yanchuk R. A. Lunin 《Journal of Experimental and Theoretical Physics》1997,85(5):989-993
The galvanomagnetic properties of single crystals of the semimagnetic semiconductors Hg1−x
MnxTe1−y
Sey with 0.01<y<0.1 and x=0.05 and 0.14 in the temperature range 4.2–300 K are investigated. The features of the temperature dependence of the Hall
coefficient R
H and the complicated behavior of R
H in a magnetic field are attributed quantitatively to the existence of three groups of current carriers, viz., electrons and
two types of holes, for which the temperature dependences of the densities and mobilities are obtained. A transition from
p-type to n-type conductivity is observed as the Se content is increased, and the negative magnetoresistance simultaneously gives way
to positive magnetoresistance.
Zh. éksp. Teor. Fiz. 112, 1809–1815 (November 1997) 相似文献
19.
The EPR of paramagnetic impurities Gd3+ and Mn2+ was studied in nonmagnetic Kondo system La1−x
CexCu6 containing in the 1.6–200 K range. The exchange interaction parameters of gadolinium and manganese ions with conduction electrons,
of cerium ions with conduction electrons and with one another, the Kondo temperature of cerium ions, and the temperature behavior
of cerium-ion spin-fluctuation rate have been determined. A pseudogap in the density of states at the Fermi level has been
detected in the CeCu6 regular system, which is apparently due to s-f hybridization. This pseudogap can be destroyed by introducing an aluminum impurity, which induces strong conduction-electron
scattering. It was also found that RKKY interaction among manganese ions in CeCu6−y
Mny is considerably stronger than it is in LaCu6−y
Mny, which implies enhancement of nonlocal spin susceptibility due to an f band contribution to conduction-electron states.
Fiz. Tverd. Tela (St. Petersburg) 40, 593–599 (April 1998) 相似文献
20.
Quantum cyclotron resonance of two-dimensional holes in strained germanium layers of the periodic heterostructure Ge-Ge1−x
Six has been observed and investigated for the first time. The results are compared with the data of electrophysical measurements
in strong magnetic fields. A clear dependence of the magnitude of the longitudinal effective mass of the holes on the absolute
magnitude of the elastic deformation of the germanium layers (splitting energy of the hole subbands) is observed.
Fiz. Tverd. Tela (St. Petersburg) 39, 2096–2100 (November 1997) 相似文献